Tag Archives: Clements

Community Development and Persistence in a Low Rocky Intertidal Zone. Jane Lubchenco and Bruce Menge (1978)

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Though I had to read through Community Development in a Low Rocky Intertidal Zone, in part or in full, several times before I feel I came to approach understanding, I feel the central idea is one of the more useful ones I’ve yet to read about for Ecological Thought and Practice. In the essay’s introduction the authors state that while communities have several characteristics, it is a mistake to study them as separate phenomena when in reality they are interconnected. In my notes, I wrote the following in order to clarify for myself what I was reading about: “Succession depends on competition (Connell) but also predation (Paine), dispersal rates and reproductive output (Gleason), life histories and persistence (Clements).

I think that due to their more holistic approach Lubchenco and Menge were able to add to ecological thought of the day by confirming and documenting the interactions among the ideas that their predecessors had proven. Though their results stated that “the role of consumers in determining the pattern followed during community development, or succession, seemed of overriding importance” which primarily confirms Paine’s 1966 essay, but predation, they found was largely inversely proportional to wave energy. They also documented, through denudation of patched of the rocks, the importance of dispersal and growth rates in determining which species became dominant, but because their study took place over several years, they were able to show the persistence of the communities and how quickly those patches returned to the state at which they had been before the experiment. This persistence supports Clements theory of a tendency toward climactic climax.

Today in class we were asked whether or not Connell and Paine’s studies contradicted one another, here Lubchenco and Menge showed that at least in some communities, the two ideas are both valid. I thought the reading was helpful in understanding other ideas we’ve already covered in class. The use of so many variables and controls including not only the exclusion of predators but the enclosure of predators were useful in illuminating the authors’ points.

Nature and Structure of the Climax. Fredric Clements (1936)

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Clements’ Nature and Structure of the Climax was concerned, as one might expect, with the state of climax of vegetation. Clements initially explains what a climax is, followed by issuing a series of questions one would ask when determining whether or not a region constitutes a climax. He goes on to argue in favor of the theory that there is only one real climax and multiple proclimaxes leading up to it. Finally explaining the structure of a climax and the roles of those species involved play.

Having not read a great deal of ecological literature previous to this, I have always imagined climax as a flash in the pan, however, in the case of ecological studies, a climax is when vegetation (over a vast area, in this reading at least) reaches a state of equilibrium. For example, a climax may be the entirety of the Great Plains in North America; every year the same plant life is dominant throughout the entirety of that area. The term biome is used instead when one is referring not only to vegetation but also animal life in a region.

Clements lays out at least four “tests” of a climax. To qualify as a climax a region must be characterized by the same form in the dominants i.e. to be considered part of a grassland climax, the dominant type of vegetation must be grass throughout. No region in which trees are dominant can be considered a portion of the grassland dominant. A region also must have the presence of the same dominant species in all or nearly all of the associations (a subdivision of a climax). Subdominants are used to link associations together, and some animals may be used as indicators too, particularly smaller, less mobile animals.

The essay goes on to argue that contrary to what Tansley said in my previous reading, there is only one kind of climax. Climax can only be used to define an area if it is one in which a community is “capable of maintaining itself under a particular climate, except where a disturbance enters.” Meaning that except in the case of the addition of a variable such as human interference, forest fire, or mass migration, a region is in a state of dynamic equilibrium. Anything appearing to be a climax that does not fit this criteria should be considered a “proclimax” defined as resembling the climax in one or more respects but gradually replaced by the latter. Of proclimaxes there are four types; subclimax, dis-, pre-, and post-. The definitions of disclimax and subclimax are clearest and best address arguments made by Tansley in 1935. Tansley referred to a “mowing” or “grazing” climax, one in which the interaction of an outside force such as a human cutting down grass or a herd eating it, reaches a sort of equilibrium with the plant life. Clements would refer to this as a disclimax, a subversion of the typical climax or succession to the climax. A preclimax is an apparent climax before the climatic climax, perhaps the climax of a particular phase of succession, or the climax of vegetation shortly after a fire, before the typical dominant again matures in the area.

Having thoroughly argued for how a climax should be described, Clements goes on to explain the structure and rolls within a climax. A dominant is the most abundant and controlling species in a climax, by which, it seems, a climax is defined. A subdominant is any species that is not the dominant. The influents are the animal species of a biome, so called because of their influence on vegetational life. The units of a climax, in descending order of importance, are, association, consociation, faciation, lociation, society, and clan. I won’t here define each, but suffice it to say that each is smaller in size than the one before and with each grade the degree of diversity allowed is greater. A more full explanation is in my notes from this reading and the most complete explanation is the text itself.

I am glad to have read this and to have more of the terms I expect to find useful defined. I agree with Gleason’s (1926) arguments as to the difficulty in defining an association or climax, though, as I mentioned in my writing about that essay I understand the utility of these definitions. If these terms are the ones we are going to be using in class, I will need to take place in a discussion about them before I feel confident enough in their meanings to use them. Regarding Clements specific argument as to the only type of climax being that of climatic climax, I disagree somewhat, as it seems to entirely ignore human interaction with the environment. I would argue that when it comes to growing crops or grazing a herd, there is an equilibrium, though a more curated one than exists in nature.

Regarding the writing in this essay, it was far more confusing than Tansley (1935) and Gleason(1926). The multitude times Clements gave examples of his theories in nature including species names may have been very helpful to someone with more information regarding those species and regions, but to me they were only confusing. Having enjoyed reading the essays by Tansley and Gleason which both refuted some of the ideas Clements had previously written, I had hoped this essay would have addressed them somewhat. Instead, Clements references The Use and Abuse Vegetational Concepts and Terms only one time, and not in any too meaningful capacity, and Gleason not at all. Of the 36 works referenced in this essay a full 11 of them are works that Clements himself is author or coauthor of. Not being well versed in ecological thought of the time I may be mistaken, but I find this absence of debate somewhat disappointing.

The Use and Abuse of Vegetational Concepts and Terms. Arthur Tansley (1935)

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Throughout this essay, Tansley argues for the standardization of the definition of several temrs commonly used in the discussion of vegetation and ecology. I will herein define in my own words what those terms are as well as discuss several of Tansleys arguments for them and some of my own thoughts on the essay.

Succession: A series of changes in the life cycle of a plant, quasi-organism, or eco-system. Each change leading to the next. The change is continuous, but can be categorized into successional phases.
Autogenic Succession: A succession primarily brought on by the actions of the plant life on their environment. E.g. A reduction in soil quality due to leeching leading to less growth.
Allogenic Succession: A succession primarily brought on by factors other than those actions of the plant life on their environment. E.g. A forest fire.
Anthrogenic Succession: A succession primarily brought on by the actions of humans on the plant life and its environment. E.g. The clearing of forest for grazing land.
Retrogressive Succession: Tansley argues that retrogressive succession is an ill-suited, though others ( use it to mean “regression” from a “higher” to “lower” form of vegetation (No clarification is given as to what higher and lower here mean) Tansley seems to say that retrogressive isn’t the correct term because the plant life is still adapting in a forward direction given the conditions of its environment at any given time.
Quasi-Organism: A mature, well-integrated plant community having enough of the characteristics of an organism. A community of plants that reaches a dynamic balance. Others use the term “complex organism”, which Tansley objects to on the grounds that an individual plant or animal is a complex organism and a network of complex organisms ought to have another name. (I initially took quasi-organism to mean the same as my understanding of an eco-system until eco-system was defined later in the text)
Climax: Permanent of apparently permanent condition reached when vegetation is in equilibrium with all Incidental factors. (There are arguably many sub-types of climax e.g. “mowing climax” a climax wherein the plant life is in a state of balance with its frequent mowing, where it doesn’t over-grow, or die off as a result of this action)
Ecosystem: The exchange among a quasi-organism and its environment. Components of which are both organic (plants, animals) and inorganic (soil, climate).
Two terms which were not defined in the text but which I found useful to look up are
Edaphic: of or relating to soil
Sere: A series of ecological communities formed in succession

My first impression of Tansley is that a contemporary reader likely would have either found him very funny or very annoying. He refers to himself twice as someone who was a heretic or who did not keep the “faith” of popular belief among ecologists of the day, instead challenging their ideas and definitions. I was intrigued by his thought on “retrogressive succession” and whether all change was necessarily “forward”, as well as the times he referred to minute and constant change in an ecosystem or quasi-organism and whether those two beliefs are related. In my notes, I likened the constant minute changes to the movement by the driver of a steering wheel on a straight road; the direction of the vehicle is always forward but the steering wheel is always being slightly turned to maintain that status. There is also the question as to whether human action can be considered part of nature, Tansley doesn’t clearly give his opinion, though through the addition of the definition of anthrogenic succession, seems to imply that humans are too great a variable to count among allogenic successions. I agree with this descision, because unlike all other animals and plants, humans don’t have to be at balance with their local environment to survive. Humans are at liberty to radically change their environment because of their ability to transport resources from afar.

Overall, I found the reading itself interesting, though, as it was my first reading of this kind, it will take me some time to be able to more fully digest its meaning and implication.